Hello, good morning from Brazil.
Yesterday, I ended up detecting a possible audio bug in notifications, whose audio notifications do not execute or are non-existent. Follow the printscreen.
For more details, try executing the default file, you will see that the audio is not executed, only if you change the file in the folder that will appear called: usr/share/sounds/freedesktop/stereo in which there are other files to be used.
I'm waiting for a possible correction or discretion of the problem.